This invention relates to transducers, or pickups, for stringed musical instruments whose output is to be electrically amplified. More particularly, the invention pertains to improved transducers providing reduction in undesirable frequency components and improved tonal qualities.
So-called electric guitars or other electrical stringed instruments develop an output for amplification by converting the vibration of the strings to an electrical signal, whose frequency spectrum corresponds to that of the vibration of the strings. Typically, such transducers, or pickups, consist of a permanent magnet element for developing a magnetic field that intercepts the strings and a coil positioned within that magnetic field. When the strings, which are of a ferromagnetic material, are plucked so as to vibrate within the magnetic field, variations in the field pattern caused by the string vibration are detected by the coils to develop an output current which follows the vibration pattern of the strings.
One of the problems encountered in connection with the electrical amplification of the output of stringed instruments is that transducers tend to pick up 60 cycle signals emanating from the power supply employed in the amplifying equipment. The 60 cycle signal is converted to an audible hum in the amplifying equipment which is annoying and degrading to the quality of the musical output. To overcome this 60 cycle hum, transducers have been developed comprising a pair of pickup coils so wound and disposed adjacent one another that the 60 cycle currents induced in the coils cancel one another, effectively eliminating 60 cycle hum from the audio output. A representative prior art patent disclosing such hum cancellation is U.S. Pat. No. 2,896,491 issued to S. E. Lover on July 28, 1959.
Prior hum elimination expedients, while effective in reducing 60 cycle hum, have disadvantages which limit their overall effectiveness. A conventional side-by-side arrangement of coils senses vibrations of each string at two relatively widely spaced points along the string, causing cancellation of certain frequencies other than the 60 cycle hum frequency and consequent degradation of musical quality. With coils mounted one on top of the other, the musical signal is not so degraded but the output signal is relatively weak.
U.S. Pat. No. 3,711,619 which issued to Jones et al on Jan. 16, 1973 discloses a pick-up device involving multiple coils in which the fidelity of sound reproduced is stated as being substantially improved over other conventional pick-up devices. In this patent, the number of turns constituting one winding are substantially different from the number of turns constituting another winding. A turns ratio of 4:1 is disclosed. The patentee discloses forming two different windings of the same size wire, although brief mention is made that different wire sizes may be employed. No special effect from the use of different size wires is disclosed. However, and in any event, the patentee completely fails to understand the hum pick-up problem which would be inherent in this arrangement involving a turns ratio of the coils other than 1:1.